Temperature compensating



Oct. 25, y1949.` K. c, DE WALT Er A| 2,486,129

TEMPERATURE COMPENSATING MECHANISM.

Filed July 264, 1946 Inventors; Kenneth C. DeWalt, Truman P; Curtis,

bgmm

ThenAtborneg. I

Patented Oct. Z5, 1949 TEMPERATURE CMPENSATING .MECHANI SM Kenneth C. De Walt and Truman P. Curtis,

Scotia, N. Y., assignors to General Electric Company, a corporation of New York Application July 26, 1946, Serial'No. 686,578

2 Claims.

Our invention relates to temperature compensating mechanisms and particularly to an improved mechanism for maintaining a predetermined or constant electrical characteristic of a device with variations in operating temperature.

Temperature compensating mechanisms havel been employed in connection with capacitors and cavity resonators for the purpose of maintaining constant characteristics with varying operating temperatures. Many of these mechanisms employ materials having different coefficients of thermal expansion in mechanical contact. With changes in temperature the contacting surfaces become loose and are dilcult to maintain in the desired positional relation.

In accordance with an important aspect of our invention all parts which have purely mechanical intcrengagement have the same coefficient of thermal expansion. The temperature compensation is accomplished by providing an insert in one of the members of the mechanism which is bonded to the end portions of that member. With this construction vvariations in the clearance between the relatively movable parts with temperature changes is avoided and the adjustment of the device is relatively easy to maintain.

It is an object of our invention to provide a new and improved temperature compensating mechanism.

It is another object of our invention to pro- Vide a new and improved temperature compensating mechanism for a cavity resonator.

It is a still further object of our invention to provide a new and improved temperature compensating mechanism in which all interengaging parte have the same coelncient of thermal expansion.

Our invention will be better understood by reference to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims, In the drawing, Fig. 1 is an elevational view, in section, of a cavity resonator embodying our invention, and Fig. 2 is a sectional View taken along the line 2-2 of Fig. 1.

Referring now to the drawing, we have shown our invention as applied to a cavity resonator which may, for example, be employed as the automatic frequency control of a microwave oscillator. As illustrated, the body of the cavity is provided by a generally rectangular metallic block I which is bored from one end to provide a cylindrical cavity 2. The block is also Icounterbored as at 3 to receive a disk-like member 4 which forms one end of the cavity, The opposite end of the block l is also provided with a bore 5 of considerably smaller diameter and a counterbore 6. As indicated,.a deformable metallic wall l is `bonded to the ledge provided at the junction of the bore ,5 and counterbore 6. A generally hollow tubular support, designated by the lnumeral 8, extends from the end of the resonator and is received within the counterbore 6. As illustrated, this support is fabricated from three Ahollow cylindrical members. An inner member ii is formed of the same material as the resonator body I and may to advantagebe of Invar steel. The intermediate section I0 of the support 8 is preferably formed of a material having a higher coeflicient of thermal expansion than the cavity and may to advantage be formed of Monel metal. The outer section of the supporting member 8 is provided by a second cylinder I I of Invar. AThe Monel cylinder I0 is bonded at its ends to the inner cylinders 9 and II in any suitable manner, 'such as by brazing. The lower end of the hollow support 8 is received within the counterbore 6 of the cavity body with the lower end thereof abutting the flexible wall 1. The-support is mechanically secured in position by'suitable set screws I2 which are threadingly received in transverse openings I3 provided in the cavity body I. The exible wall 'I and a tuning plunger I4 secured to the lower face thereof are supported from the outer cylinder I I of the support in adjustable relation thereto by a differential screw mechanism including an elongated externally threaded bolt-like member I5 bonded at its lower end to the deformable wall 'I and engaging at its upper end an internal thread provided on an adjusting screw IB. The adjusting screw is received in a threaded opening I'I provided at the lower end of the upper cylinder I! of the support 8. The threads between the members I5 and I6 and between the members I6 and II are of different pitches so that these members cooperate to provide a differential screw mechanism which as is well understood provides a fine adjustment of the flexible wall 1 and tuning plunger I4.

In order that high frequency energy may be introduced and extracted from the cavity suitable dielectric windows are provided on opposed side walls of the cavity body. As illustrated, glass windows I8 are received in recesses I9 which communicate with the interior of the cavity through openings 29.

From the foregoing detailed description of the illustrated embodiment of my invention it will be apparent that changes in operating temperature of the cavity will result in movement of the tuning plunger I4 and the deformable wall 1 with which it is connected. For example, if the operating temperature rises the operating frequency of the cavity tends to decrease. However, since the coefficient of thermal expansion of Monel considerably exceeds that of Invar, the support 8 increases in length a greater amount than the adjusting screw member I5, with the result that the tuning plunger I4 and supporting wall 1 are moved outwardly, in this way decreasing the effective capacity of the cavity and restoring the operating frequency for which the cavity has been adjusted. It is apparent that the axial length of the Monel cylinder I must be accurately determined for the particular cavity construction with which it is employed. It is also apparent that all of the parts of the compensating mechanism which are mechanically interconnected have the same coeflicient of thermal expansion. This has been found to be extremely important in that it eliminates all looseness or binding between these parts and makes it possible to maintain a setting of the mechanism once it has been made. It is possible to lock the threaded parts without accidental movement by lling the threads with a thermal setting compound of suitable character. This locking of the adjustment cannot be accomplished satisfactorily with the usual mechanisms where materials having different thermal coeiilcients of expansion are in threaded engagement.

While we have shown and described a particular embodiment of our invention, it will be obvious to those skilled in the art that changes and modications may be made without departing from our invention in its broader aspects, and we, therefore, aim in the appended claims to cover all such changes and modications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A cavity resonator including a hollow metallic structure which changes dimensions with changes in temperature, a member movable with respect to said hollow structure for compensating I6 and elongated supporting.

' electrical device asa result of changes in temperature, said device including a hollow metallic structure having a exible wall, said mechanism including a hollow elongated support having end portions formed of a material of one coefficient of thermal expansion and an intermediate portion bonded at opposite ends to said end portions and formed of a material having a coeflicient of thermal expansion diierent from said end portions, said hollow metallic structure including a wall portion joined to said iexible wall, said wall portion having the same coeicient of thermal expansion as the end portions of said hollow elonv gated support, one of said endportions being joined to said wall portion adjacent said flexible Wall and means for adjusting the positional relation of said flexible wall with respect to said metallic structure comprising an elongated member having a coefficient of thermal expansion equal to the coefoient of thermal expansion of the end portions of said hollow support and connected at one end to said flexible Wall, and means connecting said elongated member in adjustable positional relation with the other end portion of for said Achanges in dimensions, an elongated said hollow support.

KENNETH C. DE WALT. TRUMAN P. CURTIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,109,880 Dow Mar. 1, 1938 2,409,321 Stephan Oct. 15, 1946 FOREIGN PATENTS Number Country Date 500,428 Great Britain Feb. 6, 1939 

